Realistic tuning options of d3 4.2 tdi

[Bushido]

Good evening all,

I am looking to gather some serious information / input on the known options for tuning the d3 a8 4.2 tdi?

The car already has a map and I know there is an option to also map the gearbox.

But, if you had say £2-3k to spend on tuning, are there turbo upgrades etc worth looking into? Do we know what realistic figures we could likely achieve?

I know there is an argument to start looking at the s8 route, but this is an itch that is interesting me